A chucking reamer of this type has the following disadvantages, among others:
(a) The cutter device is in this case a cemented-carbide tip in the form of a reversible cutter. Cemented-carbide is both expensive and splinters like glass. Most of the volume of cemented-carbide sold is not used for cutting at all, and only a few out of every thousand perform cutting work. If the carbide tip is destroyed during use of one of its cutters, then the other cutter is also simultaneously destroyed, so that no use can be made of its reversing tip properties.
(b) Cemented-carbide has a much lower coefficient of thermal conductivity than tool steel, for example. Grinding must therefore be carried out very carefully. Chucking during grinding may also lead to fracture and also must be carried out very carefully.
(c) The carbide tip is retained in a non-positive manner by clamping. Very large forces are required for clamping, and since the carbide tip is as ground on all sides, it represents a very smooth object which is difficult to retain by clamping, in principle.
(d) The carbide tip must be wide in order to obtain sufficient clamping area. This means that a groove must be milled deeply into the head of the reamer to receive the carbide tip. Such a deep groove weakens the head, but a steeply inclined head is preferable, because chucking reamers must operate to a high degree of precision and therefore must not become deformed or distorted.
(e) The groove for receiving the carbide tip is produced by a side milling cutter. For reasons of manufacture, the groove requires an opening in the front of the head of the reamer. However, a centering hole is also required in the front of the head, because it must be possible to machine the complete chucking reamer between centers. In the case of small reamer diameters, e.g. 10 mm, the requirement for the deep groove on the one hand, and the centering hole on the other, means that a pin must be projected from the front of the head, the pin being 10 mm long, for example. This pin would in turn support the centering hole at the front. The groove would then run into the pin. The additional pin makes manufacture more expensive, and in particular it naturally obstructs the chucking reamer until the bottom of a hole is reached. The pin cut by the groove is not bend-resistant either.
(f) The crescent-shaped body is difficult to manufacture: it is machined on all sides and has an internal thread. The direction of rotation of the internal thread is opposite to the direction of rotation of the internal thread in the bottom face of the crescent-shaped recess. It includes a differential screw which is provided with two opposing threads and which draws the crescent-shaped body towards the carbide tip. Screwing in the differential screw is difficult. To ensure that the crescent-shaped body is sufficiently guided, it is provided with a collar at the end of its thread, which corresponds to a supplementary recess in the bottom face.
(g) Because of the geometry of the support faces/groove/carbide tip, the pressure pieces of the headless screws (grub screws) must have a wedge face, as shown, for example, in FIG. 2 of West German Pat. No. 1,427,182. This means higher manufacturing costs for the pressure (thrust) pieces and for correct fitting.
(h) For a number of reasons the degree of flattening of the head may be very low. This means that the cutting space will be very small, and the known chucking reamer therefore requires a special cutting chip discharge groove in the front face area.
(i) Adjustment for correct positioning of the cutting edge of the carbide tip is very complicated, lengthy and can only be carried out after special training. A special tool must be used for rapid operation. During adjustment, the pressure (thrust) piece is pressed linearly against the brittle carbide tip, with very large forces. The headless grub screws must then be rotated inwards if the diameter is to be increased. If the diameter is to be reduced, the differential screw must be loosened, the grub screws turned outwards, the carbide tip pressed so that it is pushed further into the groove, until it stops at some point inside the groove. Only then can the grub screws be turned inwards again, after the differential screw has first been tightened.
(j) Since the carbide tip must be clamped, the head cannot be hardened and must therefore remain soft.
(k) The heat dissipation from the carbide tip is unfavorable, since cemented-carbide--as stated above--has a low thermal conductivity, and since there are only a few essentially punctiform arrangements in the head.